A national advocacy group is targeting Republican Senate hopeful Mark Jacobs with a new television ad that criticizes him for what it says was his support for cap-and-trade legislation backed by President Barack Obama and congressional Democrats.

Trees of Liberty, which says it is interested in economic policy issues, began airing the ad Friday.

In it, the group highlights comments Jacobs made on a conference call in 2009 while chief executive of Houston-based Reliant Energy. Jacobs, the ad noted, said that a bill passed in the U.S. House to establish a cap-and-trade system provided a "workable framework" and a national climate change policy would "hit the mark."

The ad says the proposal would have cost thousands of Iowa jobs.

Jacobs is one of five Republicans seeking the party's nomination to replace the retiring Sen. Tom Harkin, D-Iowa.

His campaign responded in an email Friday.

"Bottom line: Mark Jacobs does not support cap-and-trade legislation. He understands how bad it is for families and businesses and would not support such legislation in the U.S. Senate. This attack by an out-of-state shadow group is exactly what is wrong with politics," the campaign said.

The email noted that Reliant had 11 coal-fired power plants that would have suffered if the legislation had been signed into law.

Trees of Liberty says it is a 501(c)(4) nonprofit organization. It has set up a website, with the ad and a news release, but the site provides little identifying information about the group or its donors.

Typically, such nonprofit advocacy groups don't identify their donors.

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A news release on the group's website lists a Mark Pfeifle as its spokesman. Pfeifle is president of Off The Record Strategies, whose website says it provides private counsel and public results.

"If we told you exactly what we do, we'd have to go on the record," says a part of the company's website.

The company's website says Pfeifle is a former national security official in the George W. Bush administration.

The ad buy is for more than $250,000 and is scheduled to run for a week.

The primary is June 3.